refactor(sdk-android): publish under io.github.priyanshujain.sanderling + ci docs fix (#27)

* refactor(sdk-android): publish under io.github.priyanshujain.sanderling

Move the published Maven coordinates to a sanderling sub-namespace so the
brand is visible in the dependency line (was io.github.priyanshujain:sdk-android).
Sub-namespace is auto-allowed by Sonatype under the verified parent groupId.

* chore: update sdk-android coordinates in folio + docs

Follow the groupId change to io.github.priyanshujain.sanderling:sdk-android.

* ci(docs): use --version flag for d2 install script

The d2 installer accepts --version vX.Y.Z, not --tag. The --tag form
was rejected as "unrecognized flag" on the docs workflow run after
PR #26 merged.

docs/manual/getting-started.md

@@ -32,7 +32,7 @@ npm install --save-dev @sanderling/spec
 
 ```kotlin
 dependencies {
-    implementation("io.github.priyanshujain:sdk-android:<version>")
+    implementation("io.github.priyanshujain.sanderling:sdk-android:<version>")
 }
 ```